On the Upper East Side of Manhattan – some 110 feet below the buildings, cars, and pedestrians – a huge project is under way to bring the new subway line to Second Avenue. Construction has been under way since 2007.

“This is the rail,” Horodniceanu said. “You can see it was delivered already.”

Phase one of the project is now two thirds complete. It will extend the Q Train from 57th Street and Seventh Avenue across town to 96th Street and Second Avenue.

Once the entire project is done, the Q Train will run northward to 125th Street in East Harlem, while a new T Train will run from 125th Street to Hanover Square in Lower Manhattan.

There has not been a subway expansion on project on such a scale since the 1940s – before the New York City Transit Authority had even yet been created. But plans for the Second Avenue Subway project go back even before that – the Second Avenue Subway was first proposed in 1929.

But now, officials said, the new subway line is desperately needed to alleviate overcrowding on the nearby No. 4, 5 and 6 lines along Lexington Avenue.

Phase one of the project calls for three brand new stations, at 72nd, 86th and 96th streets. They will serve 200,000 daily riders.